The holding of parts or articles requiring machining, such as turning, cutting, grinding, routing, drilling, milling and the like, particularly when the walls of the part or article to be machined are relatively thin walled or of honeycomb type structure or where the part or article is complex in configuration and interrupted cuts are required or involved, has presented substantial and numerous problems. Also, such problems arise where such parts or articles have open spaces that must be closed during machining to avoid contamination. The machining of such parts or articles may result in chatter, vibration, distoration of the part, fracturing and deflection as well as causing interference with the tool or machine performing the operation. Such adverse actions become particularly troublesome where automatically operated machine tools, such as those controlled by tape, microprocessors or similar means, are being used. In order to be able to produce accurate machinings of such parts or articles they must be held tightly, stabilized, supported and/or fixtured sufficiently so that there is no displacement, deflection, distortion, vibration or fracturing of their walls during the machining operation.
It has heretofore been known to utilize compositions for holding, supporting or stabilizing a wide variety of many different parts or articles during the performance of various machining operations. For example, U.S. Pat. Nos. 3,394,095 and 3,498,813, assigned to the assignee of the present application, disclose and claim compositions for this purpose, which have been successfully used commercially for about a decade. Said patents disclose particulate-filled thermoplastic compositions and their use to rigidize, support or stabilize thin walled or hollow parts or articles or parts and articles involving an interrupted cut by heating such compositions to a molten state, pouring said molten compositions into and/or around such articles before machining so as to produce a rigidly held and supported article or an effectively solid article so that the machining operations can be performed upon the article without damage to the article or in a single operation. Upon completion of the operation the machined part or article is separated from the thermoplastic composition by subjecting them to heat and/or a suitable solvent or vapor degreaser.
Although said compositions have found widespread acceptance and have enjoyed substantial commercial use certain properties of said compositions could benefit by being improved. For example, if the composition were to have a faster set time this would enable the machining operation to have a faster manufacturing cycle time. Additionally a composition of improved adhesiveness would substantially eliminate or reduce shrinkage of the composition away from the part or article during cooling following pouring of the composition in or around the part or article and thereby produce more stability and rigidity for the part or article. Moreover, since said compositions are reusable and are in fact used numerous times any increase in the stability of the composition and any stabilization of the viscosity of the composition would be highly desirable and beneficial.
Furthermore, the compositions described in the two previously mentioned United States patents include 29 to b 39% by weight of a commercially available material sold by Monsanto Chemical Corporation under the trademark "Aroclor 5460" and comprising chlorinated biphenyls and chlorinated polyphenyls. Recently environmentalists, governmental officials and other persons have been seriously questioning and objecting to the use of such polychlorinated biphenyl compositions. And, the United States Environmental Protection Agency acting under the authority of the Toxic Substance Control Act (TSCA) has defined polychlorinated biphenyls, which are specifically banned in TSCA, as being any compound containing more than 50 parts per million of polychlorinated biphenyl.
It is , therefore, highly desirable that water-insoluble, thermoplastic compositions of the type previously described and used be available which do not contain any such polychlorinated biphenyls or other polychlorinated hydrocarbon compounds which are or may become banned. It is even more desirable to be able to find a replacement for such commercially used thermoplastic compositions which are superior in performance and properties than the previously known or used compositions.